Chiang Mai Journal of Science

The stable phase equilibrium of the aqueous quaternary system Li+, K+, Mg2+ // borate-H2O at 323 K was investigated using an isothermal dissolution method. The compositions, densities and refractive indices of the solution at equilibrium were measured. The phase diagram, water content diagram and the diagrams of the physicochemical properties (density and refractive index) versus composition were obtained using the measured data. The phase diagram of this quaternary system contains one invariant point E, three univariant curves (AE, BE and CE) and three crystalline phase areas. The invariant point is co-saturated with three salts, i.e. Li2B4O7×3H2O, K2B4O7×4H2O and MgB4O7×9H2O. This quaternary system was simple and formed little double salt or solid solution. The sizes of salt crystallization areas were in the order of MgB4O7×9H2O > Li2B4O7×3H2O > K2B4O7×4H2O, which demonstrates the salt MgB4O7×9H2O can be more easily separated from the solution than the other two coexisting salts at 323 K. Comparisons between the stable phase diagrams at 323 K and 348 K show that both of K2B4O7×4H2O and Li2B4O7×3H2O crystallization zones were enlarged at 323 K, while the crystallization zones of MgB4O7×9H2O was shrinked at 323 K.